An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector including an ink pressurization chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator can be one of various types, including a heater that vaporizes some of the ink in the pressurization chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to produce a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the recording medium is moved relative to the printhead.
A common type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the recording medium and the printhead is mounted on a carriage. In a carriage printer, the recording medium is advanced a given distance along a media advance direction and then stopped. While the recording medium is stopped, the printhead is moved by the carriage in a carriage scan direction that is substantially perpendicular to the media advance direction as the drops are ejected from the nozzles. After the printhead has printed a swath of the image while traversing the recording medium, the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
In an inkjet printer, the face of the printhead die containing the nozzle array(s) is typically positioned near the recording medium in order to provide improved print quality. Close positioning of the nozzle face of the printhead die to the recording medium keeps the printed dots close to their intended locations, even for angularly misdirected jets. A flexible printed wiring member that brings electrical signals to the printhead die is typically attached adjacent to the printhead die and is electrically interconnected to the printhead die. The electrical interconnections are subsequently encapsulated for protection. An and of the flexible printing wiring member opposite the die connection region is typically disconnectably mated to an electrical connector. Typically the flexible printed wiring member is bent between the die connection region and the electrical connector region, so that the electrical connector does not interfere with the close positioning of the printhead die to the recording medium.
The connection pads at both the die connection region and the electrical connector region are typically plated with layers of nickel and gold over the patterned copper layer of the flexible printed wiring member. An insulating cover layer is typically provided over a region of the flexible printed wiring member between the die connection region and the electrical connector region in order to prevent plating of expensive metals such as gold in this region. The insulating cover layer also provides protection of the unplated copper against corrosion. However, it has been found that at boundaries between unplated copper and the copper that has been plated (i.e. near edges of the cover layer) the unplated copper can be subject to corrosion, especially in humid or moist environments. Such corrosion can adversely affect the connection reliability of the flexible printed wiring member. This can also adversely affect the reliability of an inkjet printhead having such a flexible printed wiring member.
What is needed is a flexible printed wiring member that is less susceptible to corrosion of the unplated copper, especially near electrical interconnect pads for wire bonding or for contact with an electrical connector.